Noob w/ Select issues

[eluser]fildawg[/eluser]
Hi, Please excuse the question from a noob. I'm trying to select a row from a table and then use the elements for futher logic. Here's the code:

$query = $this->db->select('code, expires_dt, amount');
$query = $this->db->from('promotions');
$query = $this->db->where('code', $coupon_code);
$query = $this->db->get();

echo 'Num_rows: ' . $query->num_rows();
echo 'Amount: '. $query->amount;

How can I access the data selected?

TIA!